1. Field of the Invention
The present invention relates to a thermal developing apparatus for heating a photosensitive thermal developing recording material to visualize a latent image recorded on an image forming layer of the photosensitive thermal developing recording material.
2. Description of the Related Art
An image forming apparatus, referred to as a medical imager, for example, forms a print of a visible image from an image measured with a medical measuring instrument, such as CT and MRI. The image forming apparatus uses a photosensitive thermal developing recording material having a support, such as a PET film, having formed thereon an image forming layer having photosensitive and thermal developing property (hereinafter, sometimes simply referred to as a recording material), and the photosensitive thermal developing recording material is imagewise exposed with a light beam modulated according to image data supplied from an image data source, such as MRT, to form a latent image thereon. Thereafter, the photosensitive thermal developing recording material thus exposed is heated to form colors with a thermal developing part incorporated in the apparatus to output a hardcopy.
The image forming apparatus of this kind is basically constituted by a recording material feeding part, an image exposing part and a thermal developing part in the order of conveying the recording material. The recording material feeding part takes out the recording material from a magazine and feeds it downstream. The image exposing part imagewise exposes the recording material by light beam scanning exposure. The thermal developing part has heating unit, for example, a heating drum, and heats the recording material to effect thermal development to convert a latent image to a visible image. Specifically, the recording material brought into the thermal developing part is conveyed with holding between the heating drum and an endless belt and is thermally developed by heat of the heating drum, whereby a latent image recorded by exposure is converted to a visible image. Accordingly, the recording material is heated with the heating drum only from one side.
In another type of the thermal developing image forming apparatus, a photosensitive material having a latent image formed through imagewise exposure is conveyed with being overlapped with an image receiving material, and the materials are thermally adhered, whereby the latent image is developed and transferred to the image receiving material, followed by detaching the photosensitive material and the image receiving material from each other. In the thermal developing image forming apparatus, a photosensitive element coated on the photosensitive material is imagewise exposed to form a latent image. The photosensitive material is then overlapped with an image receiving material, and the materials are pressed under heat between a rotating drum and an endless belt pressed on the rotating drum, whereby diffusible dyes are released from the photosensitive material in an image part and transferred to the image receiving material. Thereafter, the materials are detached from each other to form a color image on the image receiving material.
In general, a recording material having an image forming layer on only one surface thereof (single sided photosensitive film) is used in the method of recording a latent image by imagewise exposing a recording material with a light beam modulated according to image data supplied from an image data source, such as MRI. Therefore, only one surface of the material having the image forming layer provided is heated as having been described for the aforementioned conventional technique. There are some cases where the recording material is heated from the side having no image forming layer even in a thermal developing part (thermal developing apparatus), in which a single sided photosensitive film is used (i.e., an auxiliary heat source is provided on a side where no image forming layer is provided). However, temperature control of the auxiliary heat source is only for supplementarily control the heating operation of the image forming layer provided on only one surface, and there is no necessity of heating from both surfaces of the material.
In the method, in which a subject is placed between an X-ray tube and a recording material, and a latent image is recorded on the recording material with an X-ray transmitted through the subject, a recording material having image forming layers on both sides of a support (double sided photosensitive film) is used. The double sided photosensitive film is housed, upon imaging, in a cassette with fluorescent intensifying screens disposed on both front and back surfaces thereof. The fluorescent intensifying screen emits fluorescent light upon irradiating with an X-ray. The double sided photosensitive film is exposed with the fluorescent light.
In the case where a recording material having image forming layers on both surfaces is applied to the conventional thermal developing apparatus for heating only one surface of a material, heat transmission to the image forming layer on the side not heated is delayed. Due to the delay in development, deviation occurs in color tone, for example, the color of the image forming layer is discolored in brown. Furthermore, in the case where heat is not sufficiently transmitted to the image forming layer on the side not heated, development thereof becomes insufficient to cause density fluctuation, in which the density thereof is reduced.
On the other hand, in a thermal developing transferring part in a thermal developing image forming apparatus, in which a recording material is also heated from the side having no image forming layer, i.e., a image forming layer formed only on one surface is auxiliary heated, the heating operation does not intend to heat image forming layers provided on both sides, and therefore, difference in development occurs between the image forming layers on front and back surfaces to cause deviation in color tone and fluctuation in density.
The inventors have developed such a thermal developing apparatus that solve the problems associated with the aforementioned conventional technique.
FIG. 1 is a constitutional diagram showing a first embodiment of a thermal developing apparatus of the invention, and FIG. 2 is a cross sectional view of a photosensitive thermal developing recording material used therein.
In FIG. 1, a thermal developing apparatus 100 heats a photosensitive thermal developing recording material (recording material) A to visualize a latent image recorded on an image forming layer. As shown in FIG. 2, the recording material A used in the thermal developing apparatus 100 has image forming layers A2 and A2 each containing a photosensitive material provided on both the first surface as one surface (for example, a front surface) of a support A1 and the second surface as the other surface (for example, a back surface) thereof.
In the thermal developing apparatus 100, such a recording material A can be used that is a double sided photosensitive film having fluorescent intensifying screens, which are not shown in the figure, disposed on both the first and second surfaces of the recording material A. The fluorescent intensifying screen emits fluorescent light through excitation upon irradiating with an X-ray. The image forming layers A2 and A2 provided on both first and second surfaces are exposed with fluorescent light from the fluorescent intensifying screens by a small amount of an X-ray. The recording material A will be described in detail later.
The recording material A having a latent image on the image forming layer A2 is generally housed in a cassette K one by one, and it is fed to the thermal developing apparatus 100 along with the cassette K. An openable lid K1 of the cassette K thus fed to the thermal developing apparatus 100 is opened and the recording material A housed therein is taken out with taking unit using a sucking disk 41 or the like.
The thermal developing apparatus 100 may have such a structure that is installed with a magazine housing plural sheets of the recording materials A. In this case, the recording materials A each having a latent image are taken out from cassettes K and housed by stacking in the magazine in a dark room or the like. The recording materials A stacked and housed in the magazine are taken out with the sucking disk 41 one by one. A pickup roller may be used instead of the sucking disk 41.
The recording material A thus taken out is then transported to a thermal developing part 47 positioned at a downstream side of the conveying direction through a conveying roller pair 43 and a conveying guide 45. A guiding part may be provided between the conveying roller pair 43 and the thermal developing part 47 for positioning the recording material A thus taken out in the direction perpendicular to the conveying direction, whereby the recording material A is positioned with respect to the thermal developing part 47 at the downstream side.
The thermal developing part 47 has first heating unit 49a for heating the first surface of the recording material A and second heating unit 49b for heating the second surface of the recording material A, which are disposed to face each other with a conveying path C of the recording material A intervening therebetween. In this embodiment, the first heating unit 49a is constituted by a cylindrical drum 51. The second heating unit 49b is constituted by plural press rollers 53, which rotate and press the recording material A to the peripheral surface of the drum 51. The drum 51 and the press rollers 53 contain heaters H as heating sources contained therein, respectively.
In this embodiment, the drum 51 having the heater H contained therein and the press rollers 53 having the heaters H contained therein are disposed to face each other with the conveying path C intervening therebetween, whereby both the first and second surfaces of the recording material A are simultaneously heated. That is, the recording material A is transported to the conveying path C formed by the gap between the drum 51 and the press rollers 53, and conveyed by being holded with the drum 51 and the press rollers 53, so as to be thermally developed by heat from the drum 51 and the press rollers 53.
The heater H used as a heating source of the drum 51 is not particularly limited, and may be one using known heating unit, such as a heating element, e.g., nichrome wire, a light source, e.g., a halogen lamp, and means for heating with hot air.
The press roller 53 may be a metallic roller, a resin roller, a rubber roller or the like, and is disposed over the entire length of the drum 51 in the axial direction thereof. The heater H used as a heating source of the press roller 53 is also not particularly limited, and may be one using known heating unit, such as a heating element, e.g., nichrome wire.
In the thermal developing part 47, upon transporting the recording material A to the conveying path C, the first surface is pressed with the press rollers 53 to press the second surface to the drum 51, whereby both the first and second surfaces of the recording material A are simultaneously heated. According to the operation, both the surfaces of the recording material A can be heated uniformly in a short period of time. In this constitution, the drum 51 and the press rollers 53 are rotated as being synchronized with the conveying speed of the recording material A, whereby there is no deviation in relative position of the heating unit and the recording material A, and the recording material A is not scraped.
The recording material A having been developed in the thermal developing part 47 is fed to an cooling part 61 disposed at a downstream side of the conveying direction. The cooling part 61 is constituted by plural cooling rollers 63 and has such a function that the recording material A having been thermally developed is gradually cooled, and therefore, the cooling part 61 is set at such a temperature that is higher than non-heated members but is lower than the thermal developing temperature. The recording material A thus slowly cooled in the cooling part 61 is transported in the downstream side of the conveying direction with a pair of delivering rollers 65 and 67 and delivered to a tray 69.
The thermal developing apparatus 100 has a controlling part 71 for controlling the first heating unit 49a, the second heating unit 49b, and the conveying speed of the recording material A. The controlling part 71 controls the first heating unit 49a through a first temperature setting part 73, and controls the second heating unit 49b through a second temperature setting part 75. It controls a conveyance driving part 79, such as a conveying motor, through a conveying speed setting part 77. The controlling part 71 controls the temperature and the conveying speed as parameters in such a manner that the total amount of heat applied to the first and second surfaces falls within the aforementioned prescribed range.
Therefore, according to the thermal developing apparatus 100, the first and second surfaces of the recording material A are simultaneously heated, and the total amount of heat applied to the second surface is controlled with respect to the total amount of heat applied to the first surface, whereby the total amounts of heat applied to both the surfaces of the photosensitive thermal developing recording material are substantially agree with each other, and thus uniform thermal development for both the surfaces can be carried out in a short period of time.
However, the thermal developing apparatus shown in FIG. 1 is of such a type that a cassette housing a double sided photosensitive film is inserted, and has a problem in increasing the size of the apparatus.
The thermal developing part 47 also has such a defect that the apparatus is increased in size due to the use of the cylindrical drum 51.